Electric contact



May 6, 1941. A. J. McMASTER ELECTRIC commcw Filed Feb. 15, 19s? Patented May 6, 1941 FFICE ELECTRIC CONTACT Archie J. McMalter, flilhland Park, 111., assignor to G-M Laboratories, Inc., Chicago, Ill.

Application February 15, 1937, Serial No. 125,689

6 Claims.

The present invention relates to sliding electric contacts such as are used in electric commutators and the like.

Objects of the invention include the provision of a low cost contact assembly of simple, rugged and compact construction which is reliable in operation, which maintains itself in proper adjustment, which can operate over an uneven contact surface, which will establish contact through a layer of accumulated dirt, lint or muck and which in operating tends to keep itself clean. These and other objects and advantages will appear as the description proceeds.

In order better to acquaint those skilled in the art with the teachings of my present invention, and also to illustrate the manner in which my invention may be put into practice, I now shall describe certain specific embodiments thereof by way of example. However, the invention is not to be construed as limited to any particular embodiment and a description of a particular example is not intended to exclude others. In the drawing:

Fig. 1 is a general plan view of a commutator assembly including contacts embodying my present invention;

Fig. 2 is an enlarged sectional elevation of one of the contact assemblies of Fig. 1, Fig. 2 being taken along the line 2-2 of Fig. 1 looking in the direction of the arrows;

Fig. 3 is a sectional view taken along the line 33 of Fi 2;

Fig. 4 is a plan view of the detail of Figs. 2 and 3 and therefore constitutes an enlarged detail of Fig. 1;

Fig. 5 is an exploded view in perspective of the component parts of the unit contact assembly of Figs. 2, 3 and 4;

Fig. 6 is an elevational view of a commutator assembly employing contacts embodying my invention but of a somewhat modified construction;

Fig. 7 is an enlarged sectional elevational detail view of one of the contacts of the assembly of Fig. 6; and,

Fig. 8 is a sectional view taken along the line 8-8 of Fig. '7.

In Fig. 1 a circular plate l2 of insulating material carries a series of concentric contact rings l4 and also a number of contact buttons l8 spaced on a series of concentric circles so as to lie also in radial rows. A contact arm 18 of insulating material is arranged to rotate about the center 28 of the disc l2. This contact arm l8 carries ten individual contact assemblies 22 and 24.

Of these, each of five contacts 22 engages a separate one of the concentric contact rings l4, and each of five contacts 24 is adapted to engage separately the contact buttons l6 which lie in one circle. Each of the contacts 22 is connected to one of the contacts'24 by means of wire connector 26. As the contact arm l8 rotates about the center 20 the five contacts 24 are brought into successive engagement with the contacts l8 of the separate radial rows whereby each of the contact rings is successively connected electrically to separate ones of the contacts It. The commutator disc l2 and contact arm l3 constitute parts of a multiple circuit step switch or indexing switch. The arm is adapted to be indexed to move the contacts 24 from one row of contact buttons 16 to the next. The manner in which the disc 12 and contact arm l8 are supported and rotated relative to each other forms no part of the present invention and a description thereof is unnecessary.

The details of the construction of one of the contacts 24 are shown in the enlarged view of Figs. 2, 3 and 4. A metal bushing 28 having shoulder 23 is riveted in a hole in the insulating contact arm i8 by staking at 30. This bushing 28 has a pair of internal opposed flutes 32 broached therein, and a metal slider or plunger 34 of phosphor bronze slides easily in the flutes 32. The slider 34 consists of a thin 'flat strip of phosphor bronze oi uniform width having a soldering eye 36 at its upper end and an enlarged contact portion 38 swedged thin at its lower end. The swedging hardens the metal of the contact portion 38 to improve its wearing qualities and also thins the contact as best shown in Fig. 2 to accentuate its knife like character. A coil compression spring 48 is interposed between the shoulder 29 of the bushing 28 and the shoulder formed by the enlargement 38 at the contact portion of the slider 34. This spring urges the slider 34 in the direction of its contact portion 38 so as to hold the contact portion 38 firmly in engagement with the disc l2 and the contact buttons l8 disposed thereon.

As the contact arm l8 rotates, the contact portionsv 38 ride across the contact buttons i8 and across the surface of the disc l2 between contact buttons l6.

As is shown in Fig. 1, the contact sliders 34 and the contact portions 38 thereof are oriented in the contact arm l8 so that the knife like edge of the contact portion 38 lies in the direction of the motion of the contact assembly 24 relative to the disc l2.

The present construction provides the spring l. with ample size and volume so that the spring may be designed to provide ample contact pressure while having a low modulus. Accordingly the present construction provides ample and substantially uniform contact pressure in spite of variations in the spacing between contact arm II and disc I2. The firm contact pressure together with the knife-like edge of the contact portion 88 enable the switch to make reliable contact even though the surface of disc I! and contact buttons ll be covered with alayer of a muck-like mixture of grease with lint and dirt. It is desirable in a low cost switch that grease be applied to the contact surfaces in lieu of plating them with noncorrosive metals. and the accumulation of some lint and dirt on a greasy surface is unavoidable.

Inasmuch as the contact portion 38 is required to engage separately a large number of contacts ll as it moves around the disc l2, each of the contact portions 88 is subjected to considerably more wear than is any one of the contact buttons ll. Because the contact portion 88 is hardened by swedging as described, it is prevented from wearing more rapidly than the contact buttons II with which it engages. The curvature of the contact portion II, the easy action of plunger 34 in bushing II and the uniform pressure of spring I all combine to make the contact plunger 84 ride easily up onto the buttons I! which protrude above the surface of the disc i2.

I The connecting wire 28 soldered to the plunger 84 at eye 38 prevents the plunger 34 from dropping out of the bushing I8 should the contact arm I! be separated from the disc II.

The present invention provides a'contact assembly giving a knife-like contact whose tension may be easily regulated in production, whose moving parts are small and rigid, which is simple in construction and which is entirely reliable in operation. In addition, the construction is compact so that a large number of contacts may be grouped in a small space.

Fig. 6 is an elevational view of a modified construction. In Fig. 6 a rotatable contact arm 44 includes a pair of parallel similar insulating strips 68 and II which are spaced apart slightly by means of spacers ii and 52. These insulating strips 48 and 48 carry a number of contact sliders I. The construction of these sliders and the manner in which they are supported in the insulating strips 48 and 48 is best seen in the enlarged sectional views of Figs. 7 and 8. The contact slider or plunger I4 is reciprocably carried in a pair of slots I8 and 58 in the strips 4 and 48 respectively. A swedged contact portion ill is provided at the lowermost end of the contact slider 84 and a soldering eye 82 is provided at its upper end. A pair of shoulders 84 extend laterally from the slider ll intermediate its ends. The apparatus is assembled so that these shoulders 84 come in the space between the two insulating strips 48 and 48 of the rotatable contact arm 44. An helical compression spring 88 is interposed between the strip 40 and the shoulders 84 to urge the contact slider downward into firm engagement with a cooperating contact button 88 in a contact plate 10. Like the spring 40 of Figs. 2 and 3, spring 88 has a low modulus so as to provide a firm uniform contact pressure regardless of the position of plunger 54 in the slots 56 and II in the separate strips 48 and 48. The strips l8 and 48 are so located relative to each other that the direction in which the slider ll reciprocates in the contact arm 44 is inclined slightly to bring the upper end of the slider 54 sl g y behind the lower or contact end of the slider with respect to the direction in which the contact 80 moves across the contact button I8. As viewed in Fig. 8 contact piece 54 is intended to move toward the right with respect to its cooperating contact, and accordingly its upper end is slightly to the left of its lower end ill. As the two strips 48 and 48 carry the contact slider- 54 toward the right as viewed in Fig. 8, the contact portion II rides on and of! the contact rivets I8. Whenever the contact portion ill encounters a rise or bump such as one of the contact buttons 68, the resistance to the forward motion caused by that bump produces a component of force tending to lift the contact slider 84 against the force of the spring 84. Accordingly any resistance encountered by the contact portion 80 against forward motion, that is, motion towards the right, as viewed in Fig. 8, tends to lift the contact portion 8. over the obstruction which causes that resistance. Therefore the inclined contact -piece ll moves from one contact to the other more easily than does the erect arrangement shown in Figs. 2 and 3.

The inclined contact plunger of Figs. 7 and 8 is particularly adapted to operate with a minimum resistance to forward motion over rough and uneven commutator surfaces, but is generally limited to motion in only one direction. The erect contact plunger of the construction of Figs. 2 and 8 is adapted to move in either direction relative to the contact disc I2.

The construction of Figs. 6, 7 and 8 wherein the contact slider I! is supported directly in the insulating contact arm 54 is particularly adapted for use when a large number of identical units are to be manufactured. It employs a somewhat simpler construction than the arrangement of Figs. 1 to 5, inclusive, but it requires more complete and precise tools for the convenient and accurate punching of the slots 58 and 58 to insure that the contacts will be properly aligned in the completed assembly. The construction of Figs. 1 to 5 inclusive, wherein the contact slider is carried in internal flutes in a circular bushing is particularly adapted for use in apparatus where comparatively small numbers of identical units are to be built. The contact assembly can be mounted easily in a contact arm such as contact arm ll wherever a plain round hole of proper size can be provided.

While I have shown and described certain specific illustrative embodiments of my present invention, it will be apparent that such embodiments are by way of example only, and are capable of many modifications and variations. For example, the bushing construction of Figs. 1 to 5 may be inclined in the same manner as is the non-bushing construction of Figs. 6 to 8, and if desired, contact slider 54 of Figs. 6 to 8 may be made erect or inclined at any other convenient angle. Accordingly, I do not intend to be limited except by the scope of the appended claims. The term knife-like edge or knife-like portion is employed to mean an edge or portion in which the longitudinal dimension is appreciably greater than the transverse dimension, and wherein the latter dimension is small enough whereby to facilitate breaking through a layer of foreign matter lying on the surface of a cooperating contact and the opposite dimension is great enough to promote sliding action.

I claim:

1. In combination in a sliding electrical contact, a guide, movable means for supporting said guide, an elongated metal plunger longitudinally reciprocable in said guide, said plunger having a knife-like contact portion on an end thereof aligned in the direction of movement thereof resulting from movement of said guide supporting means, means urging said plunger in the direction of said knife-like contact portion, said knifellke contact portion adapted to engage a stationary contact member with a sliding action whereby to cause said knife-like portion to cut through surface matter on the stationary contact whereby to form good electrical engagement between said stationary contact and said knife-like contact portion, and an uneven contact surface over which the said knife-like contact portion of said elongated metal plunger is adapted to slide, said guide being tilted with respect to the direction of sliding so that the end of said guide nearest said contact surface moves in advance of the other end thereof.

2. In combination, a sliding electric contact and a contact surface over which said sliding contact is adapted to slide, said sliding contact including: a guide, an elongated plunger longitudinally reciprocable in said guide toward and away from said contact surface, said plunger having a contact end adapted to engage said contact surface, and means yieldably urging said contact end of said plunger into engagement with said contact surface, said guide being so inclined to the direction of motion of said sliding contact relative to said contact surface that said contact end of said plunger leads.

3. In combination, two contact support members, means for supporting said contact support members to permit relative movement therebetween while maintaining the distance of their separation substantially constant, a plurality of aligned contact members fixed to one of said contact support members, a plurality of metal sliders carried by the other contact support member, each having a knife-like contact portion adapted to engage a plurality of said aligned contacts, said knife edge being aligned in the direction of relative movement with the said aligned contacts whereby to engage said contacts with a knife-like cutting action and cut through non-conductable surface matter, guide means to prevent movement of said metal sliders except in a direction longitudinal thereof whereby said alignment in the direction of relative movement is maintained, said guide means forming a part of said second contact support member and including fluted portions in which the said sliders have longitudinal movement, spring means urging said sliders in the direction of said first-mentioned aligned contact members, said second-mentioned contact support member including two spaced strips having aligned, keyed apertures therein, said slider being reciprocable in said apertures, and said apertures comprising said guide means.

4. In combination in a'slidin electric contact, a contact support member consisting of two spaced strips having aligned apertures therein, an elongated integral thin fiat bronze slider longitudinally reciprocable in said apertures, said slider having a curved end constituting a knife like contact portion, said slider being swedged hard at said end whereby the metal of said contact portion is hard, said slider having integral lateral projections, and a coil compression spring encircling said slider and interposed between said projections and one of the strips of said support.

5. In combination in a sliding electric contact, a disc of insulating material, a plurality of buttoncontacts supported in an orderly path on one face of said disc, a contact arm of sheet-like insulating material pivoted to rotate about an axis vertical to said disc at a mid-point thereof, whereby said arm is adapted to move in a plane parallel to the plane of said disc, at least one bushing secured to extend through said contact arm at a position to follow the path defined by said button contacts on said disc when said contact arm is moved relatively to said disc, said bushing having a pair of opposed internal flutes together defining a slot extending longitudinally through said bushing and through said contact arm, a metal slider in the form of a flat strip slidable in the slot defined by the flutes in said bushing, said slider extending entirely through said bushing and being of uniform transverse di mension except for integral projections near that end thereof extending toward said button con tacts, and a coil spring surrounding said bush ing and slider and having one end engaging said projections to force said slider in a direction to Ward said button contacts, said slider having a knife-like edge at that end thereof adapted to engage said button contacts, and said edge being aligned in the direction of movement thereof.

6. The combination defined in claim 5, wherein said bushing comprises a metal part of generally tubular form with an outside annular shoulder, said shoulder bearing against one face of the sheet-like material comprising said arm, and an integral out-flared portion engaging against the opposite face of said sheet-like material comprising said arm.

ARCHIE J. MCMASTER. 

